I will use a specific antiserum against Lyb3 surface component to isolate mature and immature subsets of B lymphocytes from CBA/H mice and to study their immunobiological properties, compared to B cells of immunodeficient CBA/N mice. I will test these B cell subsets with respect to quantitative and qualitative antibody production in a response to thymus-dependent and thymus-independent antigens and with respect to the ease of tolerance induction. Ontological studies of the appearance of Lyb3 ion B cells will help delineate B cell maturation and diversification. Further, I will analyze the mechanism of antigen dependent triggering by anti-Lyb3. I will test its triggering capacity in combination with different antigenic signals and by its ability to induce a high avidity memory response in the absence of T cells. I will also characterize the metabolic events during this triggering reaction. The quantitative expression of Lyb3 on B cells at different stages of antigen-induced activation will provide insight in the possible role that Lyb3 plays in the immune function of the cell. Biochemical characterization of the Lyb3 molecule-will be done with the goal of purifying enough Lyb3 for direct functional studies.